Introdução ao DAS e SCSI

Transcription

1 06 infra TI Introdução ao DAS e SCSI DAS; Elements, Benefits and Challenges; Management options; Evolution of SCSI; SCSI 3 architecture; SCSI addressing and communication model; DAS e SCSI comparation

2 What is DAS? Uses block level protocol for data access Internal Direct Connect External Direct Connect

3 DAS Benefits Ideal for local data provisioning Quick deployment for small environments Simple to deploy Low capital expense Low complexity

4 DAS Connectivity Options ATA (IDE) and SATA Primarily for internal bus SCSI Parallel (primarily for internal bus) Serial (external bus) FC High speed network technology Buss and Tag Primarily for external mainframe Precursor to ESCON and FICON

5 DAS Management Internal Host provides: Disk partitioning (Volume management) File system layout Direct Attached Storage managed individually through the server and the OS External Array based management Lower TCO (Total Cost of Ownership) for managing data and storage Infrastructure

6 DAS Challenges Scalability is limited Number of connectivity ports to hosts Difficulty to add more capacity Limited bandwidth Distance limitations Downtime required for maintenance with internal DAS Limited ability to share resources Array front-end port Unused resources cannot be easily re-allocated Resulting in islands of over and under utilized storage pools

7 Evolution of Parallel SCSI ANSI acknowledged SCSI as an industry standard Developed by Shugart Associates & named as SASI (Shugart Associates System Interface) SCSI versions SCSI 1 Defined cable length, signaling characteristics, commands & transfer modes Used 8-bit narrow bus with maximum data transfer rate of 5 MB/s SCSI 2 Defined Common Command Set (CCS) to address non-standard implementation of the original SCSI Improved performance, reliability, and added additional features SCSI 3 Latest version of SCSI Comprised different but related standards, rather than one large document

8 SCSI 3 Architecture SCSI command protocol Primary commands common to all devices Transport layer protocol Standard rules for device communication and information sharing Physical layer interconnect Interface details such as electrical signaling methods and data transfer modes SCSI Architectural SCSI-3 Command Model Protocol SCSI Primary Command s SCSI Specific Commands Common Access Method Transport Layer SCSI-3 Protoco l Physical Layer SCSI-3 Parallel Interfac e Fibre Channel Protoco l IEEE Serial Bus Serial Bus Protoco l Fibre Channe l Generi Packetized Protoco c l

9 SCSI Device Model SCSI communication involves: SCSI initiator device Issues commands to SCSI target devices Example: SCSI host adaptor SCSI target device Executes commands issued by initiators Examples: SCSI peripheral devices SCS Initiator Device I Application Client Device Service Reques t Device Service Response Task Management Reques t Task Management Response SCS Target I Device Logical Unit Device Server Tas Manager k

10 SCSI Device Model (Cont.) Device requests uses Command Descriptor Block (CDB) 8 bit structure Contain operation code, command specific parameter and control parameter SCSI Ports SCSI device may contain initiator port, target port, target/initiator port Based on the port combination, a SCSI device can be classified as an initiator model, a target model, a target model with multiple ports or a combined model (target/initiator model). Example: Target/initiator device contain target/initiator port and can switch orientations depending on the role it plays while participating in an I/O operation To cater to service requests from multiple devices, a SCSI device may also have multiple ports (e.g. target model with multiple ports)

11 SCSI Addressing Initiator Target LUNs Initiator ID Target ID LUN Initiator ID - a number from 0 to 15 with the most common value being 7. Target ID - a number from 0 to 15 LUN - a number that specifies a device addressable through a target.

12 SCSI Addressing Example Port Target (Front-end port) Target t0 Port Port Port Port LUN LUN LUN d0 d1 d2 Storage Volumes Host Initiator (HBA) Controller c0 Storage Array Host Addressing: Storage Volume 1 - c0t0d0 Storage Volume 2 - c0t0d1 Storage Volume 3 - c0t0d2 Initiator ID Target ID LUN c0 t0 d0

13 Discussão e exercícios Em que cenários devemos empregar soluções de DAS? Quais as vantagens oferecidas pelas conexões de armazenamento SCSI e em que cenários melhor de aplicam? Conexões paralelas são sempre mais rápidas que conexões seriais? Há um algum paralelo dos protocolos SCSI com os protocolos de rede de comunicações de dados (TCP/IP)? Qual o papel de um iniciator device?

14 Leitura recomendada Capítulo 5 Information Storage and Management Storing, Managing, and Protecting Digital Information in Classic, Virtualized, and Cloud Environments 2nd Edition Edited by Somasundaram Gnanasundaram, Alok Shrivastava